Observations on the development of the excretory system in Turtles. 701 



blastema surrounding the ureter and probably also as branches 

 from it. 



4. If the foregoing hold true, then pronephros, mesonephros and 

 metanephros are heterodynamous, not homodynamous organs, con- 

 nected alone by their relations to the Wolffian duct. 



5. The glomus of the pronephric region is distinct in origin, 

 character, position and extent from the glomerulus of the metanephros. 



Literature. 



Among the most important papers on the urinogenital system of 

 Reptiles are those of Max Braun ^), C. K. Hoffmann 2) and of 

 R. WiEDERSHEiM ^). Max Braun used lizards and snakes and C. M. 

 Hoffmann lizards. Max Braun gives a review of all the literature 

 preceding his article, and is in turn, with others, reviewed by Hoff- 

 mann. Braun was the first to establish the development of the ureter 

 from the dorsal side of the Wolffian duct. The basis of the meta- 

 nephros, he finds in disconnected strands of cells. He thinks they 

 originate from the peritoneum, but as they extend beyond the region 

 of the body cavity, Hoffmann questions it. Both Braun and Hoff- 

 mann find the metanephric tubules developing as branches from the 

 ureter. 



Hoffmann has earlier stages and finds (p. 264) "die erste An- 

 lage bei Lacerta ayïlis in der Bildung einer segmentirten Falte oder 

 einer Reihe segmentaler Ausstülpungen der Somatopleura, welche sich 

 dort bildet, wo der Somit in die Seitenplatte übergeht; dieselbe er- 

 streckt sich unter 6 — 7 Somiten , die Zahl derselben scheint nicht 

 immer constant zu sein", and on page 265: "Es scheint mir nun wohl 

 nicht zweifelhaft, dass diese ... die Anlage eines rudimentären Pro- 

 nephros vorstellt." He finds also that the posterior of these grows 

 backwards and forms the "Anlage" of the Wolffian duct and unites 

 so closely with the ectoderm that it is difficult to tell whether it is 

 a case of true fusion or not. The later stages of the pronephros 

 seem to be quite ditferent in lizards from the conditions I find in 

 turtles. He finds the "Anlage" of the mesonephros just as it is de- 



1) Das Urogenitalsystem der einheimischen Reptilien , in : Arb. 

 zool.-zoot. Inst. Würzburg, 1877 — 78, V. 4. 



2) Zur Entwicklungsgeschichte der Urogenitalorgane bei den Rep- 

 tilien, in: Z. wiss. Zool., V. 48, 1889. 



3) Ueber die Entwicklung des Urogenitalapparats bei Crocodilen 

 und Schildkröten, in : Arch. mikr. Anat., V. 36, 1 890. 



